In the emerging “hydrogen economy,” it is anticipated that hydrogen gas will be a very widely used fuel, perhaps the fuel of choice for millions of fuel cells that could be used in vehicles, portable electronic devices, and small motorized devices (lawn mowers, snow blowers, and the like). However, there remain safety concerns about using hydrogen as fuel for these purposes. Hydrogen gas can leak through the tiniest imperfections in tanks, lines, or joints. Accumulated hydrogen is extremely flammable and, because it is odorless and colorless, hydrogen gas gives no warning of its presence.
There has been considerable interest in developing chemical compounds that can be added to hydrogen that provide an easily detectable and recognizable odor so that anyone with a normal sense of smell could tell immediately if there were a hydrogen leak in the vicinity and take corrective action before an explosion or fire occurred. This approach has been used for many years to make natural gas and household gas immediately recognizable in the event of a gas leak or if a gas appliance (a gas furnace, gas stove, and the like) is releasing the gas, which has greatly contributed to the safe use and widespread acceptance of gas in households.
There are problems associated with adding odorants to hydrogen. Many odorizing compounds contain sulfur or nitrogen. These odorants cannot be used with devices such as fuel cells. Typical fuel cells have a platinum anode, and these types of odorants can “poison” the platinum anode or the electrolyte membrane and degrade the fuel cell's performance, even if present in very small amounts. For fuel cells that operate at lower temperatures, an odorant will not ordinarily be destroyed as it passes through the fuel cell into the exhaust, so some additional means must be taken to remove the odorant and prevent the normal exhaust from being mistaken for a hydrogen leak. In addition, hydrogen is so buoyant in air that leaking hydrogen and most of any odorant added to the hydrogen will float to accumulate in headspace. If this happens, there is risk that dangerous amounts of hydrogen will accumulate in the headspace before the odor of odorant additives can be noticed.
There are other fluids besides hydrogen that do not possess a distinctive odor or color and that are therefore difficult for people to detect directly, where the intended use of the substance does not easily admit adding an odorizing compound, and where a leak could be harmful or dangerous. One such substance is methanol. Methanol is used in direct-methanol fuel cells and other devices. Methanol is toxic, and ingesting sub-lethal doses has caused blindness, so consumers generally are concerned about exposure to methanol.
A material that could be applied to a surface of the container, to the container housing, to pipes, fittings, or other connections to the container, or to surfaces near the container as a coating that would respond to fluids such as hydrogen and/or methanol by chemically reacting with the fluid to produce a color change or release an detectable odorant could alert people to a leak yet not require anything being added directly to the fluid itself.